As the wireless market rapidly has grown in recent years, a need has arisen for a single wireless transceiver IC that can work with several different wireless protocols, more particularly Bluetooth and 802.11b. Prior art implementations for standalone Bluetooth or 802.11b transceivers are known. Typically, direct-conversion or other RF conversion techniques perform a simple frequency translation between RF and baseband. Post-conversion, most of the channel-select filtering and amplification is carried out in the baseband.
Bluetooth receive (RX) mode, a typically 2.4 GHz RF signal is down-converted to 2 MHz low-IF for channel-select band-pass filtering, limiting, and subsequent band-pass filtering suppresses harmonics from the previous limiting operation. The resultant signals are then passed to a subsequent GFSK demodulator stage.
Using 802.11b protocol, in wireless-LAN (WLAN) RX mode, RF signals are down-converted to DC for channel-select low-pass filtering. The converted signals are then processed through signal amplitude-controlled variable gain amplifiers (VGA's).
Common analog/digital (A/D) converters may be used for the Bluetooth and 802.11b protocol signals to quantize I/Q outputs for equalization and demodulation. Exemplary prior art design approaches for complex filters suitable for Bluetooth transceiver applications may be found in J. Crols and M. Steyaert, “Low-IF Topologies for High-Performance Analog Front Ends of Fully Integrated Receivers,” IEEE Trans. Circuits Syst.-II, vol.45, pp. 269-282, March 1998, herein incorporated by reference.
The most straightforward approach to provide dual functionality found in the prior art appears to be placing a Bluetooth transceiver IC and a separate 802.11b transceiver IC on a single chip, such as system 100 shown in FIG. 1. Bluetooth filter and amplifier 105 and a separate wireless LAN filter and amplifier 110 are coupled to an RF transmit/receive unit 120 and a digital baseband unit 130. In the system 100, select control signal 135 is applied to switches 140 and 145 to select either the Bluetooth filter and amplifier unit 105 or the wireless LAN filter and amplifier unit 110. To implement the Bluetooth unit 105 and the wireless LAN unit 110, all components for both units are fabricated and laid out separately, consuming chip area.
What is needed is a dual-mode Bluetooth/802.11b baseband circuit that can be implemented with a single IC. Preferably the resultant transceiver would provide a reconfigurable analog baseband that includes a single dual-mode complex filter system, and a single dual-mode amplifier system. Such an IC should be implementable with reduced chip area.
The present invention provides such a dual-mode analog baseband circuit.